Automatic transmission

ABSTRACT

There is provided an automatic transmission capable of preventing deterioration of driving performance even when an engagement mechanism is not switched due to a failure. An automatic transmission includes a first brake which is always in a fixed state from a first forward gear stage to a predetermined gear stage and is in an open state at a gear stage with a higher speed than the predetermined gear stage, and a hydraulic sensor configured to detect whether the first brake is switched to the fixed state. When a transmission control device instructs the first brake to switch to the fixed state, and it is confirmed that the first brake is in an open state, the transmission control device instructs engagement mechanisms other than the first brake to perform switching so that a preliminary gear stage is able to be set.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Japan application serialno. 2017-069044, filed on Mar. 30, 2017. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND Technical Field

The disclosure relates to an automatic transmission mounted in avehicle.

Description of Related Art

In the related art, an automatic transmission that is mounted in avehicle and can convert an output of a driving source and transmit it todrive wheels is known (for example, refer to Patent Document 1). Aplurality of clutches and brakes are provided in the automatictransmission and the clutches and brakes are controlled by an operationhydraulic pressure.

Patent Documents

[Patent Document 1] Japanese Unexamined Patent Application Laid-Open(JP-A) No. 2016-098987

SUMMARY

An automatic transmission that sets a plurality of gear stages bychanging a combination of a plurality of engagement mechanisms that areput into an engaged state or a fixed state among engagement mechanismssuch as clutches and brakes may include a first engagement mechanismwhich is always in one state of an open state and an engaged state or afixed state in all of a first gear stage group from a first forward gearstage to a predetermined forward intermediate gear stage among theplurality of gear stages.

In such an automatic transmission, when the first engagement mechanismhas failed and cannot be switched to one state, it is possible to setonly a gear stage (a gear stage with a higher speed than a gear stage ofa forward low gear range) with a lower gear ratio than a forwardintermediate gear stage, it is difficult to start the vehicle, and thevehicle may not be able to travel uphill.

In addition, the automatic transmission may include a second engagementmechanism that is in one state of an open state and an engaged state ora fixed state only at a gear stage (hereinafter referred to as astarting gear) set when a vehicle starts forward movement and in anotherstate of an open state and an engaged state or a fixed state in othergear stages. In such an automatic transmission, when the secondengagement mechanism cannot be switched from one state to the otherstate due to a failure, there is a problem that only the starting gearcan be set and a vehicle can travel only at a low speed.

The embodiments of the invention have been made in view of the abovecircumstances, and an object of the embodiments of the invention is toprovide an automatic transmission capable of preventing deterioration ofdriving performance even when an engagement mechanism is not switcheddue to a failure.

In order to achieve the above object, one or some exemplary embodimentof the invention provides an automatic transmission (for example, anautomatic transmission 3 of an embodiment; hereinafter the same) thatincludes a plurality of engagement mechanisms (for example, clutches C1to C3 or brakes B1 to B3 of an embodiment; hereinafter the same) thatare switchable between one state of an open state and an engaged stateor a fixed state and another state thereof; and a control unit (forexample, a transmission control device ECU of an embodiment; hereinafterthe same) configured to instruct the engagement mechanisms to switch tothe one state or the other state. The control unit sets a plurality ofgear stages (for example, a first gear to a tenth gear of an embodiment;hereinafter the same) by changing a combination of a plurality ofengagement mechanisms that are put into an engaged state or a fixedstate among the engagement mechanisms. The automatic transmissionincludes a first engagement mechanism (for example, a first brake B1 ofan embodiment; hereinafter the same) which is any one of the pluralityof engagement mechanisms, wherein the first engagement mechanism is inone state (for example, a fixed state of an embodiment; hereinafter thesame) of an open state and an engaged state or a fixed state in all of afirst gear stage group (for example, a first forward gear stage to afifth forward gear stage of an embodiment; hereinafter the same) from afirst forward gear stage to a predetermined gear stage (for example, thefifth gear of an embodiment; hereinafter the same) among the pluralityof gear stages, and is in the other state (for example, an open state ofan embodiment; hereinafter the same) at a gear stage with a higher speedthan the predetermined gear stage, and a state determination unit (forexample, a hydraulic sensor or a hydraulic switch of an embodiment;hereinafter the same) configured to detect whether the first engagementmechanism has switched to the one state. When the control unit instructsthe first engagement mechanism to switch to the one state, and the statedetermination unit confirms that the first engagement mechanism is inthe other state, the control unit instructs the engagement mechanismsother than the first engagement mechanism to perform switching so that apreliminary gear stage (for example, a 2.5^(th) gear of an embodiment;hereinafter the same) is able to be set, wherein the preliminary gearstage is other than those in the plurality of gear stages and is able tobe set when the first engagement mechanism is in the other state. Thepreliminary gear stage is a gear stage with a low speed that has a gearratio equal to or greater than a gear ratio of the predetermined gearstage.

According to one or some exemplary embodiments of the invention, evenwhen the first engagement mechanism has failed and cannot be switched toone state, it is possible to set a preliminary gear stage that is a gearstage (a gear stage at which travelling is possible at a speed equal toor lower than a speed of a predetermined gear stage) with a higher gearratio than the predetermined gear stage. Therefore, according to thepreliminary gear stage, it is possible to travel uphill and it ispossible to prevent deterioration of driving performance.

In addition, in one or some exemplary embodiments of the invention, theautomatic transmission includes a housing (for example, a transmissioncase 10 of an embodiment; hereinafter the same), an input unit (forexample, an input shaft 11 of an embodiment; hereinafter the same) thatis rotatably disposed inside the housing, an output unit (for example,an output member 13 of an embodiment; hereinafter the same), and fourplanetary gear mechanisms (for example, first to fourth planetary gearmechanisms PG1, PG2, PG3, and PG4 of an embodiment; hereinafter thesame) that each include three elements including a sun gear (forexample, sun gears Sa, Sb, Sc, and Sd of an embodiment; hereinafter thesame), a carrier (for example, carriers Ca, Cb, Cc, and Cd of anembodiment; hereinafter the same) and a ring gear (for example, ringgears Ra, Rb, Rc, and Rd of an embodiment; hereinafter the same). Thethree elements of the third planetary gear mechanism are a firstelement, a second element, and a third element in an arrangement orderat intervals corresponding to a gear ratio in a collinear diagram thatis able to express a relative rotation speed ratio by a straight line.The three elements of the fourth planetary gear mechanism are a fourthelement, a fifth element, and a sixth element in an arrangement order atintervals corresponding to a gear ratio in a collinear diagram. Thethree elements of the first planetary gear mechanism are a seventhelement, an eighth element, and a ninth element in an arrangement orderat intervals corresponding to a gear ratio in a collinear diagram. Thethree elements of the second planetary gear mechanism are a tenthelement, an eleventh element, and a twelfth element in an arrangementorder at intervals corresponding to a gear ratio in a collinear diagram.The first element is connected to the input unit, the tenth element isconnected to the output unit, the second element, the fifth element, andthe ninth element are connected to form a first connected body, thethird element and the twelfth element are connected to form a secondconnected body, and the eighth element and the eleventh element areconnected to form a third connected body. The engagement mechanismincludes three clutches (for example, first to third clutches C1 to C3of an embodiment; hereinafter the same), three brakes (for example,first to third brakes B1 to B3 of an embodiment; hereinafter the same),and a two-way clutch (for example, a two-way clutch F1 of embodiment;hereinafter the same). The first clutch is switchable between aconnected state in which the first element and the third connected bodyare connected and an open state in which the connection is disconnected.The second clutch is switchable between a connected state in which thesixth element and the second connected body are connected and an openstate in which the connection is disconnected. The third clutch isswitchable between a connected state in which the first element and thefourth element are connected and an open state in which the connectionis disconnected. The first brake is switchable between a fixed state inwhich the seventh element is fixed to the housing and an open state inwhich the fixed state is released. The second brake is switchablebetween a fixed state in which the sixth element is fixed to the housingand an open state in which the fixed state is released. The third brakeis switchable between a fixed state in which the fourth element is fixedto the housing and an open state in which the fixed state is released.The two-way clutch is switchable between a reverse rotation preventionstate in which forward rotation of the third connected body is allowedand reverse rotation is prevented and a fixed state in which rotation ofthe third connected body is prevented. The first engagement mechanism isthe first brake. The one state is the open state. According to one orsome exemplary embodiments of the invention, the preliminary gear stageis a gear stage set when the second clutch and the third brake are putinto an engaged state and the other engagement mechanisms are put intoan open state.

According to one or some exemplary embodiments of the invention, evenwhen the first brake cannot be switched to an engaged state due to afailure of the automatic transmission and the first brake remains in anopen state, it is possible to set a preliminary gear stage that is agear stage (a gear stage at which travelling is possible at a speedequal to or lower than a speed of a predetermined gear stage) with ahigher gear ratio than the predetermined gear stage. Therefore,according to the preliminary gear stage, it is possible to travel uphilland it is possible to prevent deterioration of driving performance.

In addition, one or some exemplary embodiments of the invention providean automatic transmission that includes a plurality of engagementmechanisms that are switchable between one state of an open state and anengaged state or a fixed state and another state; and a control unitconfigured to instruct the engagement mechanisms to switch to the onestate or the other state. The control unit sets a plurality of gearstages by changing a combination of a plurality of engagement mechanismsthat are put into an engaged state or a fixed state among the engagementmechanisms. The automatic transmission includes a second engagementmechanism (for example, a two-way clutch F1 of an embodiment;hereinafter the same) which is any one of the plurality of engagementmechanisms, wherein the second engagement mechanism is in the one stateonly at a starting gear which is a gear stage set upon departure amongthe plurality of gear stages in one of forward and reverse movement, andis in the other state at a gear stage with a higher speed than thestarting gear, and a state determination unit configured to detectwhether the second engagement mechanism has switched to the other state.When the control unit instructs the second engagement mechanism toswitch to the other state, and the state determination unit confirmsthat the second engagement mechanism is in the one state, the controlunit instructs the engagement mechanisms other than the secondengagement mechanism to perform switching so that a preliminary gearstage is able to be set, wherein the preliminary gear stage is otherthan those in the plurality of gear stages and is able to be set whenthe second engagement mechanism is in the one state. The preliminarygear stage is a gear stage with a higher speed than the starting gear.

According to one or some exemplary embodiments of the invention, evenwhen the second engagement mechanism cannot be switched to the otherstate due to a failure, it is possible to set a preliminary gear stagethat is a gear stage (a gear stage at which travelling is possible at aspeed that exceeds a speed of the starting gear) with a lower gear ratiothan the starting gear. Accordingly, even in a failure, it is possibleto travel at a preliminary gear stage faster than the starting gear, andit is possible to prevent deterioration of driving performance.

In addition, in one or some exemplary embodiments of the invention, theautomatic transmission includes a housing, an input unit that isrotatably disposed inside the housing, an output unit; and fourplanetary gear mechanisms (first to fourth planetary gear mechanisms)that each include three elements including a sun gear, a carrier, and aring gear. The three elements of the third planetary gear mechanism area first element, a second element, and a third element in an arrangementorder at intervals corresponding to a gear ratio in a collinear diagramthat is able to express a relative rotation speed ratio by a straightline. The three elements of the fourth planetary gear mechanism are afourth element, a fifth element, and a sixth element in an arrangementorder at intervals corresponding to a gear ratio in a collinear diagram.The three elements of the first planetary gear mechanism are a seventhelement, an eighth element, and a ninth element in an arrangement orderat intervals corresponding to a gear ratio in a collinear diagram. Thethree elements of the second planetary gear mechanism are a tenthelement, an eleventh element, and a twelfth element in an arrangementorder at intervals corresponding to a gear ratio in a collinear diagram.The first element is connected to the input unit, the tenth element isconnected to the output unit, the second element, the fifth element, andthe ninth element are connected to form a first connected body, thethird element and the twelfth element are connected to form a secondconnected body, and the eighth element and the eleventh element areconnected to form a third connected body. The engagement mechanismincludes three clutches (first to third clutches), three brakes (firstto third brakes), and a two-way clutch. The first clutch is switchablebetween a connected state in which the first element and the thirdconnected body are connected and an open state in which the connectionis disconnected. The second clutch is switchable between a connectedstate in which the sixth element and the second connected body areconnected and an open state in which the connection is disconnected. Thethird clutch is switchable between a connected state in which the firstelement and the fourth element are connected and an open state in whichthe connection is disconnected. The first brake is switchable between afixed state in which the seventh element is fixed to the housing and anopen state in which the fixed state is released. The second brake isswitchable between a fixed state in which the sixth element is fixed tothe housing and an open state in which the fixed state is released. Thethird brake is switchable between a fixed state in which the fourthelement is fixed to the housing and an open state in which the fixedstate is released. The two-way clutch is switchable between a reverserotation prevention state in which forward rotation of the thirdconnected body is allowed and reverse rotation is prevented and a fixedstate in which rotation of the third connected body is prevented. Thesecond engagement mechanism is the two-way clutch. According to one orsome exemplary embodiments of the invention, the preliminary gear stageis a gear stage set when the second clutch and the third brake are putinto an engaged state and the other engagement mechanisms are put intoan open state.

According to one or some exemplary embodiments of the invention, evenwhen the two-way clutch cannot be switched to a reverse rotationprevention state due to a failure, it is possible to set a preliminarygear stage that is a gear stage (a gear stage at which travelling ispossible at a speed that exceeds a speed of the starting gear) with alower gear ratio than the starting gear. Accordingly, even in a failure,it is possible to travel at a preliminary gear stage faster than thestarting gear, and it is possible to prevent deterioration of drivingperformance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram schematically showing a vehicle inwhich an automatic transmission of an embodiment is mounted.

FIG. 2 is a skeleton diagram showing the automatic transmission of thepresent embodiment.

FIG. 3 is a collinear diagram of a planetary gear mechanism of thepresent embodiment.

FIG. 4 is an explanatory diagram showing an engaged state of engagementmechanisms at gear stages of the present embodiment.

FIG. 5 is an explanatory diagram showing a fixed state of a two-wayclutch of the present embodiment in a cross section.

FIG. 6 is an explanatory diagram showing a reverse rotation preventionstate of the two-way clutch of the present embodiment in a crosssection.

FIG. 7 is a perspective view showing a fixed state of the two-way clutchof the present embodiment.

FIG. 8 is a perspective view showing a reverse rotation prevention stateof the two-way clutch of the present embodiment.

FIG. 9 is an explanatory diagram showing the automatic transmission ofthe present embodiment.

FIG. 10 is a flowchart showing operations of a control unit of theautomatic transmission of the present embodiment.

FIG. 11 is an explanatory diagram showing rotational speeds of elementswhen the 2.5^(th) gear is set in a collinear diagram of the planetarygear mechanism of the present embodiment.

DESCRIPTION OF THE EMBODIMENTS

An automatic transmission of an embodiment and a vehicle in which thetransmission is mounted will be described with reference to thedrawings.

As shown in FIG. 1, in a vehicle V in which the automatic transmissionof the present embodiment is mounted, an engine E (an internalcombustion engine as a driving source; an electric motor may be used inplace of the engine E) is mounted in a vehicle body sideways so that acrankshaft 1 is directed in the left to right direction in the vehiclebody. A driving force output from the engine E is transmitted to a powertransmission device PT. Then, the power transmission device PT adjusts adriving force of the engine E according to a selected gear ratio andtransmits it to left and right front wheels WFL and WFR.

The power transmission device PT includes an automatic transmission 3having a torque converter 2 connected to the crankshaft 1 and a frontdifferential gear 4 connected to the automatic transmission 3.

The front differential gear 4 is connected to the left and right frontwheels WFL and WFR through a front left axle 7L and a front right axle7R.

FIG. 2 is a skeleton diagram showing a part of the automatictransmission 3 excluding the torque converter 2. The automatictransmission 3 includes an input shaft 11 that is rotatably pivotallysupported in a transmission case 10 as a housing, as an input member towhich a driving force output from the engine E is transmitted throughthe torque converter 2 including a lock-up clutch and a damper, and anoutput member 13 including an output gear that is disposedconcentrically with the input shaft 11.

Rotation of the output member 13 is transmitted to left and right drivewheels (the front wheels WFL and WFR) of a vehicle through an idle gear21 meshed with the output member 13, an idle shaft 23 pivotallysupporting the idle gear 21, a final drive gear 25 pivotally supportedon the idle shaft 23, and the front differential gear 4 including afinal driven gear 27 meshed with the final drive gear 25. Here, in placeof the torque converter 2, a frictionally engageable single plate typeor multi-plate type starting clutch may be provided. In addition, apropeller shaft can be connected in place of the front differential gear4 and applied to a rear wheel drive vehicle. In addition, a propellershaft can be connected to the front differential gear 4 via a transferand applied to a four-wheel drive vehicle.

In addition, the automatic transmission 3 of the present embodimentincludes a parking lock mechanism 40. A parking gear 42 of the parkinglock mechanism 40 is fixed to and rotates together with the idle shaft23. A parking pole 44 pivotally supported on a support shaft 44 a isdisposed in the vicinity of the parking gear 42. A locking claw 46 isprovided at an end on the side of the parking gear 42 of the parkingpole 44. When the locking claw 46 is engaged with the parking gear 42,the state is put into a state (parking locked state) in which drivewheels (front wheels WFL and WFR) are unable to rotate through the idleshaft 23. The parking pole 44 is biased by a release spring 48 in adirection in which the locking claw 46 releases from the parking gear42.

A cam 50 is disposed at the other end of the parking pole 44 in a freelymoving forward and backward manner. When the cam 50 moves forward, theparking pole 44 swings against a biasing force of the release spring 48,and the locking claw 46 is engaged with the parking gear 42. When thecam 50 moves backward, the parking pole 44 returns to an originalposition due to a biasing force of the release spring 48, and thelocking claw 46 and the parking gear 42 are disengaged.

A parking piston 54 is connected to the cam 50 via a link 52. Theparking piston 54 is movable in its own axial direction due to ahydraulic pressure. Then, when the parking piston 54 moves in the axialdirection, the cam 50 moves forward and backward via the link 52.

Inside the transmission case 10 as a housing, four planetary gearmechanisms (first to fourth planetary gear mechanisms PG1 to PG4) aredisposed concentrically with the input shaft 11 in order from a drivingsource ENG side.

The first planetary gear mechanism PG1 is a so-called single pinion typeplanetary gear mechanism which includes a sun gear Sa, a ring gear Ra,and a carrier Ca that pivotally supports a pinion Pa meshed with the sungear Sa and the ring gear Ra rotatably and revolvingly.

The so-called single pinion type planetary gear mechanism is also calleda minus planetary gear mechanism or a negative planetary gear mechanismbecause the ring gear rotates in a direction different from that in thesun gear when the carrier is fixed and the sun gear is rotated. Here, inthe so-called single pinion type planetary gear mechanism, when the ringgear is fixed and the sun gear is rotated, the carrier rotates in thesame direction as the sun gear.

With reference to a collinear diagram of the first planetary gearmechanism PG1 shown in the third part from the top in FIG. 3, when thethree elements Sa, Ca, and Ra of the first planetary gear mechanism PG1are referred to as a seventh element, an eighth element, and a ninthelement from the left side, respectively, in the order of arrangement atintervals corresponding to the gear ratio in the collinear diagram, theseventh element is the sun gear Sa, the eighth element is the carrierCa, and the ninth element is the ring gear Ra. A ratio between aninterval between the sun gear Sa and the carrier Ca and an intervalbetween the carrier Ca and the ring gear Ra is set to h:1 when the gearratio of the first planetary gear mechanism PG1 is h.

The second planetary gear mechanism PG2 is a so-called single piniontype planetary gear mechanism which includes a sun gear Sb, a ring gearRb, and a carrier Cb that pivotally supports a pinion Pb meshed with thesun gear Sb and the ring gear Rb rotatably and revolvingly.

With reference to a collinear diagram of the second planetary gearmechanism PG2 shown in the fourth part (the bottom part) from the top inFIG. 3, when the three elements Sb, Cb, and Rb of the second planetarygear mechanism PG2 are referred to as a tenth element, an eleventhelement, and a twelfth element from the left side, respectively, in theorder of arrangement at intervals corresponding to the gear ratio in thecollinear diagram, the tenth element is the ring gear Rb, the eleventhelement is the carrier Cb, and the twelfth element is the sun gear Sb. Aration between an interval between the sun gear Sb and the carrier Cband an interval between the carrier Cb and the ring gear Rb is set toi:1 when the gear ratio of the second planetary gear mechanism PG2 is i.

The third planetary gear mechanism PG3 is a so-called single pinion typeplanetary gear mechanism which includes a sun gear Sc, a ring gear Rc,and a carrier Cc that pivotally supports a pinion Pc meshed with the sungear Sc and the ring gear Rc rotatably and revolvingly.

With reference to a collinear diagram (a diagram that can express ratiosbetween relative rotational speeds of the three elements including thesun gear, the carrier, and the ring gear by straight lines (speedlines)) of the third planetary gear mechanism PG3 shown in the secondpart from the top in FIG. 3, when the three elements Sc, Cc, and Rc ofthe third planetary gear mechanism PG3 are referred to as a firstelement, a second element, and a third element from the left side,respectively, in the order of arrangement at intervals corresponding tothe gear ratio (the number of teeth of the ring gear/the number of teethof the sun gear) in the collinear diagram, the first element is the sungear Sc, the second element is the carrier Cc, and the third element isthe ring gear Rc.

Here, a ratio between an interval between the sun gear Sc and thecarrier Cc and an interval between the carrier Cc and the ring gear Rcis set to j:1 when the gear ratio of the third planetary gear mechanismPG3 is j. Here, in the collinear diagram, the lower horizontal line andthe upper horizontal line (lines overlapping 4^(th) and 6^(th)) indicatea rotational speed of “0” and “1” (the same rotational speed as theinput shaft 11), respectively.

The fourth planetary gear mechanism PG4 is a so-called single piniontype planetary gear mechanism which includes a sun gear Sd, a ring gearRd, and a carrier Cd that pivotally supports a pinion Pd meshed with thesun gear Sd and the ring gear Rd rotatably and revolvingly.

With reference to a collinear diagram of the fourth planetary gearmechanism PG4 shown in the first part (the top part) from the top inFIG. 3, when the three elements Sd, Cd, and Rd of the fourth planetarygear mechanism PG4 are referred to as a fourth element, a fifth element,and a sixth element from the left side, respectively, in the order ofarrangement at intervals corresponding to the gear ratio in thecollinear diagram, the fourth element is the ring gear Rd, the fifthelement is the carrier Cd, and the sixth element is the sun gear Sd. Aratio between an interval between the sun gear Sd and the carrier Cd andan interval between the carrier Cd and the ring gear Rd is set to k:1when the gear ratio of the fourth planetary gear mechanism PG4 is i.

The sun gear Sc (the first element) of the third planetary gearmechanism PG3 is connected to the input shaft 11. In addition, the ringgear Rb (the tenth element) of the second planetary gear mechanism PG2is connected to the output member 13 including an output gear.

In addition, the carrier Cc (the second element) of the third planetarygear mechanism PG3, the carrier Cd (the fifth element) of the fourthplanetary gear mechanism PG4, and the ring gear Ra (the ninth element)of the first planetary gear mechanism PG1 are connected to form a firstconnected body Cc-Cd-Ra. In addition, the ring gear Re (the thirdelement) of the third planetary gear mechanism PG3 and the sun gear Sb(the twelfth element) of the second planetary gear mechanism PG2 areconnected to form a second connected body Rc-Sb. In addition, thecarrier Ca (the eighth element) of the first planetary gear mechanismPG1 and the carrier Cb (the eleventh element) of the second planetarygear mechanism PG2 are connected to form a third connected body Ca-Cb.

In addition, the automatic transmission of the present embodimentincludes seven engagement mechanisms including three first to thirdclutches C1 to C3, three first to third brakes B1 to B3, and one two-wayclutch F1.

The first clutch C1 is a hydraulically actuated wet multi-plate clutchand is switchable between a connected state in which the sun gear Sc(the first element) of the third planetary gear mechanism PG3 and thethird connected body Ca-Cb are connected and an open state in which theconnection is disconnected.

The third clutch C3 is a hydraulically actuated wet multi-plate clutchand is switchable between a connected state in which the sun gear Sc(the first element) of the third planetary gear mechanism PG3 and thering gear Rd (the fourth element) of the fourth planetary gear mechanismPG4 are connected and an open state in which the connection isdisconnected.

The second clutch C2 is a hydraulically actuated wet multi-plate clutchand is switchable between a connected state in which the sun gear Sd(the sixth element) of the fourth planetary gear mechanism PG4 and thesecond connected body Rc-Sb are connected and an open state in which theconnection is disconnected.

The two-way clutch F1 also has a function as a fourth brake B4, andallows forward rotation (rotation direction of the input shaft 11 and/orrotation in the same direction as a rotation direction of the outputmember 13 when a vehicle moves forward) of the third connected bodyCa-Cb, and is switchable between a reverse rotation prevention state inwhich reverse rotation (in a direction of rotation opposite to forwardrotation) is prevented and a fixed state in which the third connectedbody Ca-Cb is fixed to the transmission case 10.

In the reverse rotation prevention state, when a rotational force in aforward rotation direction is applied to the third connected body Ca-Cb,the two-way clutch F1 is put into an open state in which the rotation isallowed, and when a rotational force in a reverse rotation direction isapplied, the two-way clutch F1 is put into a fixed state in which therotation is prevented and the third connected body Ca-Cb is fixed to thetransmission case 10. That is, the two-way clutch F1 automaticallyswitches between a fixed state and an open state in the reverse rotationprevention state. In the present embodiment, the two-way clutchcorresponds to a second engagement mechanism of the embodiments of theinvention.

The first brake B1 is a hydraulically actuated wet multi-plate clutchand is switchable between a fixed state in which the sun gear Sa (theseventh element) of the first planetary gear mechanism PG1 is fixed tothe transmission case 10 and an open state in which the fixed state isreleased.

The second brake B2 is a hydraulically actuated wet multi-plate clutchand is switchable between a fixed state in which the sun gear Sd (thesixth element) of the fourth planetary gear mechanism PG4 is fixed tothe transmission case 10 and an open state in which the fixed state isreleased. The third brake B3 is a hydraulically actuated wet multi-plateclutch and is switchable between a fixed state in which the ring gear Rd(the fourth element) of the fourth planetary gear mechanism PG4 is fixedto the transmission case 10 and an open state in which the fixed stateis released.

States of the clutches C1 to C3 and the brakes B1 to B3, and the two-wayclutch F1 are switched on the basis of vehicle information such as atravel speed of a vehicle transmitted from an integrated control unit(not shown) by a transmission control device ECU including atransmission control unit (TCU) shown in FIG. 1.

The transmission control device ECU includes an electronic unitconstituted by a CPU, a memory, and the like (not shown), and canreceive predetermined vehicle information such as a travel speed and anaccelerator opening of the vehicle V, a rotational speed and an outputtorque of the engine E, and operation information of a paddle shiftlever 33, and execute a control program stored in a storage device suchas a memory in the CPU, and thus controls the automatic transmission 3(transmission mechanism).

As shown in FIG. 1, the paddle shift lever 33 is provided on a handle 31of the vehicle V of the present embodiment, upshifting is performed by amanual operation when a right paddle 33 u is pulled forward, anddownshifting is performed by a manual operation when a left paddle 33 dis pulled forward. An operation signal of the paddle shift lever 33 istransmitted to the transmission control device ECU.

Here, an operation unit for performing a manual operation is not limitedto the paddle shift lever 33 of the embodiment. Another operation unit,for example, a shift lever disposed between a driver's seat and apassenger's seat or a button disposed on a handle may be used.

As shown in FIG. 2, on the axis of the input shaft 11, from the side ofthe driving source ENG and the torque converter 2, the first clutch C1,the first planetary gear mechanism PG1, the second planetary gearmechanism PG2, the third planetary gear mechanism PG3, the second clutchC2, the fourth planetary gear mechanism PG4, and the third clutch C3 aredisposed in that order.

Then, the third brake B3 is disposed radially outward from the fourthplanetary gear mechanism PG4, the second brake B2 is disposed radiallyoutward from the second clutch C2, the first brake B1 is disposedradially outward from the first clutch C1, and the two-way clutch F1 isdisposed radially outward from the first planetary gear mechanism PG1.

In this manner, when the three brakes B1 to B3 and the two-way clutch F1are disposed radially outward from a planetary gear mechanism or aclutch, it is possible to reduce the axial length of the automatictransmission 3 compared with when the brakes B1 to B3 and the two-wayclutches F1 are disposed in parallel along the axis of the input shaft11 together with the planetary gear mechanisms and the clutches. Here,the third brake B3 may be disposed radially outward from the thirdclutch C3 and the second brake B2 may be disposed radially outward fromthe fourth planetary gear mechanism PG4.

Next, a case in which gear stages of the automatic transmission 3 of theembodiment are set will be described with reference to FIG. 3 and FIG.4.

In order to set a first gear, the two-way clutch F1 is put into areverse rotation prevention state (R in FIG. 4) and the first brake B1and the second brake B2 are put into a fixed state. When the two-wayclutch F1 is put into a reverse rotation prevention state (R) and thefirst brake B1 is put into a fixed state, reverse rotation of the thirdconnected body Ca-Cb and the sun gear Sa (the seventh element) of thefirst planetary gear mechanism PG1 are prevented, and rotational speedsof the third connected body Ca-Cb and the sun gear Sa (the seventhelement) of the first planetary gear mechanism PG1 are “0.”

Accordingly, three elements (seventh to ninth elements Sa, Ca, and Ra)of the first planetary gear mechanism PG1 are put into a locked state inwhich relative rotation is not possible, and a rotational speed of thefirst connected body Cc-Cd-Ra including the ring gear Ra (the ninthelement) of the first planetary gear mechanism PG1 is “0.” Then, arotational speed of the ring gear Rb (the tenth element) of the secondplanetary gear mechanism PG2 to which the output member 13 is connectedbecomes “1st” shown in FIG. 3 and the first gear is set.

Here, in order to set the first gear, it is not necessary to set thesecond brake B2 in a fixed state. However, the second brake B2 is set inthe first gear in a fixed state so that shifting from the first gear toa second gear to be described below can be performed smoothly. Inaddition, in order for an engine brake to be effective in the firstgear, the two-way clutch F1 may be switched from a reverse rotationprevention state (R) to a fixed state (L).

In order to set the second gear, the two-way clutch F1 is put into areverse rotation prevention state (R), the first brake B1 and the secondbrake B2 are put into a fixed state, and the second clutch C2 is putinto a connected state. When the two-way clutch F1 is put into a reverserotation prevention state, forward rotation of the third connected bodyCa-Cb is allowed. In addition, when the first brake B1 is put into afixed state, a rotational speed of the sun gear Sa (the seventh element)of the first planetary gear mechanism PG1 is “0.” In addition, when thesecond brake B2 is put into a fixed state, a rotational speed of the sungear Sd (the sixth element) of the fourth planetary gear mechanism PG4is “0.”

In addition, when the second clutch C2 is put into a connected state, arotational speed of the second connected body Rc-Sb is “0” that is thesame speed as a rotational speed of the sun gear Sd (the sixth element)of the fourth planetary gear mechanism PG4. Then, a rotational speed ofthe ring gear Rb (the tenth element) of the second planetary gearmechanism PG2 to which the output member 13 is connected is “2^(nd)”shown in FIG. 3, and the second gear is set.

In order to set a third gear, the two-way clutch F1 is put into areverse rotation prevention state, the first brake B1 and the secondbrake B2 are put into a fixed state, and the third clutch C3 is put intoa connected state. When the two-way clutch F1 is put into a reverserotation prevention state, forward rotation of the third connected bodyCa-Cb is allowed. In addition, when the first brake B1 is put into afixed state, a rotational speed of the sun gear Sa (the seventh element)of the first planetary gear mechanism PG1 is “0.” In addition, when thesecond brake B2 is put into a fixed state, a rotational speed of the sungear Sd (the sixth element) of the fourth planetary gear mechanism PG4is “0.”

In addition, when the third clutch C3 is put into a connected state, arotational speed of the ring gear Rd (the fourth element) of the fourthplanetary gear mechanism PG4 is “1” that is the same speed as arotational speed of the sun gear Sc (the first element) of the thirdplanetary gear mechanism PG3 connected to the input shaft 11. Since arotational speed of the sun gear Sd (the sixth element) of the fourthplanetary gear mechanism PG4 is “0” and a rotational speed of the ringgear Rd (the fourth element) is “1,” a rotational speed of the carrierCd (the fifth element), that is, a rotational speed of the firstconnected body Cc-Cd-Ra is k/(k+1).

Then, a rotational speed of the ring gear Rb (the tenth element) of thesecond planetary gear mechanism PG2 to which the output member 13 isconnected is “3^(rd)” shown in FIG. 3, and the third gear is set.

In order to set a fourth gear, the two-way clutch F1 is put into areverse rotation prevention state, the first brake B1 is put into afixed state, and the second clutch C2 and the third clutch C3 are putinto a connected state. When the two-way clutch F1 is put into a reverserotation prevention state, forward rotation of the third connected bodyCa-Cb is allowed. In addition, when the first brake B1 is put into afixed state, a rotational speed of the sun gear Sa (the seventh element)of the first planetary gear mechanism PG1 is “0.”

In addition, when the second clutch C2 is put into a connected state,the sun gear Sd (the sixth element) of the fourth planetary gearmechanism PG4 and the second connected body Rc-Sb rotate at the samespeed. Accordingly, between the third planetary gear mechanism PG3 andthe fourth planetary gear mechanism PG4, the carrier Cc (the secondelement) and the carrier Cd (the fifth element) are connected, and thering gear Rc (the third element) and the sun gear Sd (the sixth element)are connected. In the fourth gear in which the second clutch C2 is putinto a connected state, one collinear diagram including four elementscan be drawn by the third planetary gear mechanism PG3 and the fourthplanetary gear mechanism PG4.

Then, when the third clutch C3 is put into a connected state, arotational speed of the ring gear Rd (the fourth element) of the fourthplanetary gear mechanism PG4 is “1” that is the same speed as arotational speed of the sun gear Sc (the first element) of the thirdplanetary gear mechanism PG3, and rotational speeds of two elementsamong four elements constituted by the third planetary gear mechanismPG3 and the fourth planetary gear mechanism PG4 are the same speed of“1.”

Accordingly, elements of the third planetary gear mechanism PG3 and thefourth planetary gear mechanism PG4 are put into a locked state in whichrelative rotation is not possible, and rotational speeds of all elementsof the third planetary gear mechanism PG3 and the fourth planetary gearmechanism PG4 are “1.” Then, a rotational speed of the third connectedbody Ca-Cb is h/(h+1), and a rotational speed of the ring gear Rb (thetenth element) of the second planetary gear mechanism PG2 to which theoutput member 13 is connected is “4^(th)” shown in FIG. 3, and thefourth gear is set.

In order to set a fifth gear, the two-way clutch F1 is put into areverse rotation prevention state, the first brake B1 is put into afixed state, and the first clutch C1 and the third clutch C3 are putinto a connected state. When the two-way clutch F1 is put into a reverserotation prevention state, forward rotation of the third connected bodyCa-Cb is allowed. In addition, when the first brake B1 is put into afixed state, a rotational speed of the sun gear Sa (the seventh element)of the first planetary gear mechanism PG1 is “0.”

In addition, when the first clutch C1 is put into a connected state, arotational speed of the third connected body Ca-Cb is “1” that is thesame speed as a rotational speed of the sun gear Sc (the first element)of the third planetary gear mechanism PG3. Then, a rotational speed ofthe ring gear Rb (the tenth element) of the second planetary gearmechanism PG2 to which the output member 13 is connected is “5^(th)”shown in FIG. 3, and the fifth gear is set.

Here, in order to set the fifth gear, it is not necessary to set thethird clutch C3 in a connected state. However, since it is necessary toset the third clutch C3 in a connected state in the fourth gear and asixth gear to be described below, the fifth gear is also put into aconnected state so that downshifting from the fifth gear to the fourthgear and upshifting from the fifth gear to the sixth gear to bedescribed below are performed smoothly.

In order to set the sixth gear, the two-way clutch F1 is put into areverse rotation prevention state and three clutches (first to thirdclutches C1 to C3) are put into a connected state. When the two-wayclutch F1 is put into a reverse rotation prevention state, forwardrotation of the third connected body Ca-Cb is allowed.

In addition, when the second clutch C2 and the third clutch C3 are putinto a connected state, as described in the fourth gear, elements of thethird planetary gear mechanism PG3 and the fourth planetary gearmechanism PG4 are put into a state in which relative rotation is notpossible and a rotational speed of the second connected body Re-Sb is“1.” In addition, when the first clutch C1 is put into a connectedstate, a rotational speed of the third connected body Ca-Cb is “1.”

Accordingly, in the second planetary gear mechanism PG2, the carrier Cb(the eleventh element) and the sun gear Sb (the twelfth element) are thesame speed of “1,” and elements are put into a locked state in whichrelative rotation is not possible. Then, a rotational speed of the ringgear Rb (the tenth element) of the second planetary gear mechanism PG2to which the output member 13 is connected is “1” of “6^(th)” shown inFIG. 3, and the sixth gear is set.

In order to set a seventh gear, the two-way clutch F1 is put into areverse rotation prevention state, the second brake B2 is put into afixed state, and the first clutch C1 and the third clutch C3 are putinto a connected state. When the two-way clutch F1 is put into a reverserotation prevention state, forward rotation of the third connected bodyCa-Cb is allowed.

In addition, when the second brake B2 is put into a fixed state, arotational speed of the sun gear Sd (the sixth element) of the fourthplanetary gear mechanism PG4 is “0.” In addition, when the third clutchC3 is put into a connected state, a rotational speed of the ring gear Rd(the fourth element) of the fourth planetary gear mechanism PG4 is “1”that is the same speed as a rotational speed of the sun gear Sc (thefirst element) of the third planetary gear mechanism PG3, and arotational speed of the first connected body Cc-Cd-Ra including thecarrier Cd (the fifth element) of the fourth planetary gear mechanismPG4 is k/(k+1).

In addition, when the first clutch C1 is put into a connected state, arotational speed of the third connected body Ca-Cb is “1” that is thesame speed as a rotational speed of the sun gear Sc (the first element)of the third planetary gear mechanism PG3 connected to the input shaft11. Then, a rotational speed of the ring gear Rb (the tenth element) ofthe second planetary gear mechanism PG2 to which the output member 13 isconnected is “7^(th)” shown in FIG. 3, and the seventh gear is set.

In order to set an eighth gear, the two-way clutch F1 is put into areverse rotation prevention state, the second brake B2 is put into afixed state, and the first clutch C1 and the second clutch C2 are putinto a connected state. When the two-way clutch F1 is put into a reverserotation prevention state, forward rotation of the third connected bodyCa-Cb is allowed.

In addition, when the second brake B2 is put into a fixed state, arotational speed of the sun gear Sd (the sixth element) of the fourthplanetary gear mechanism PG4 is “0.” In addition, when the second clutchC2 is put into a connected state, a rotational speed of the secondconnected body Rc-Sb is “0” that is the same speed as a rotational speedof the sun gear Sd (the sixth element) of the fourth planetary gearmechanism PG4.

In addition, when the first clutch C1 is put into a connected state, arotational speed of the third connected body Ca-Cb is “1” that is thesame speed as a rotational speed of the sun gear Sc (the first element)of the third planetary gear mechanism PG3. Then, a rotational speed ofthe ring gear Rb (the tenth element) of the second planetary gearmechanism PG2 to which the output member 13 is connected is “8^(th)”shown in FIG. 3, and the eighth gear is set.

In order to set a ninth gear, the two-way clutch F1 is put into areverse rotation prevention state, the second brake B2 and the thirdbrake B3 are put into a fixed state, and the first clutch C1 is put intoa connected state. When the two-way clutch F1 is put into a reverserotation prevention state, forward rotation of the third connected bodyCa-Cb is allowed.

In addition, when the second brake B2 is put into a fixed state, arotational speed of the sun gear Sd (the sixth element) of the fourthplanetary gear mechanism PG4 is “0.” In addition, when the third brakeB3 is put into a fixed state, a rotational speed of the ring gear Rd(the fourth element) of the fourth planetary gear mechanism PG4 is “0.”Therefore, elements Sd, Cd, and Rd of the fourth planetary gearmechanism PG4 are put into a locked state in which relative rotation isnot possible, and a rotational speed of the first connected bodyCc-Cd-Ra including the carrier Cd (the fifth element) of the fourthplanetary gear mechanism PG4 is “0.”

In addition, when the first clutch C1 is put into a connected state, arotational speed of the third connected body Ca-Cb is “1” that is thesame speed as a rotational speed of the sun gear Sc (the first element)of the third planetary gear mechanism PG3. Then, a rotational speed ofthe ring gear Rb (the tenth element) of the second planetary gearmechanism PG2 to which the output member 13 is connected is “9^(th)”shown in FIG. 3, and the ninth gear is set.

In order to set a tenth gear, the two-way clutch F1 is put into areverse rotation prevention state, the third brake B3 is put into afixed state, and the first clutch C1 and the second clutch C2 are putinto a connected state. When the two-way clutch F1 is put into a reverserotation prevention state, forward rotation of the third connected bodyCa-Cb is allowed.

In addition, when the second clutch C2 is put into a connected state,the second connected body Rc-Sb and the sun gear Sd (the sixth element)of the fourth planetary gear mechanism PG4 rotate at the same speed. Inaddition, when the third brake B3 is put into a fixed state, arotational speed of the ring gear Rd (the fourth element) of the fourthplanetary gear mechanism PG4 is “0.” In addition, when the first clutchC1 is put into a connected state, a rotational speed of the thirdconnected body Ca-Cb is “1” that is the same speed as a rotational speedof the sun gear Sc (the first element) of the third planetary gearmechanism PG3. Then, a rotational speed of the ring gear Rb (the tenthelement) of the second planetary gear mechanism PG2 to which the outputmember 13 is connected is “10^(th)” shown in FIG. 3, and the tenth gearis set.

In order to set a reverse gear, the two-way clutch F1 is put into afixed state (L in FIG. 4), the second brake B2 is put into a fixedstate, and the third clutch C3 is put into a connected state. When thesecond brake B2 is put into a fixed state and the third clutch C3 is putinto a connected state, a rotational speed of the first connected bodyCc-Cd-Ra is k/(k+1). In addition, when the two-way clutch F1 is put intoa fixed state, a rotational speed of the third connected body Ca-Cb is“0.” Then, a rotational speed of the ring gear Rb (the tenth element) ofthe second planetary gear mechanism PG2 to which the output member 13 isconnected is reverse rotation “Rvs” shown in FIG. 3, and the reversegear is set.

Here, speed lines indicated by dashed lines in FIG. 3 indicate thatelements of other planetary gear mechanisms rotate (idle) following aplanetary gear mechanism that transmits power among the four planetarygear mechanisms PG1 to PG4.

FIG. 4 is a diagram collectively showing states of the clutches C1 toC3, the brakes B1 to B3, and the two-way clutch F1 at theabove-described gear stages. “O” in the columns of the three clutches(first to third clutches C1 to C3), and the three brakes (first to thirdbrakes B1 to B3) indicate a connected state or a fixed state, and blankcolumns indicate an open state. In addition, “R” in the column of thetwo-way clutch F1 indicates a reverse rotation prevention state and “L”indicates a fixed state.

In addition, the underlined “R” and “L” indicate that a rotational speedof the third connected body Ca-Cb is “0” due to the action of thetwo-way clutch F1. In addition, “R/L” indicates a state that is areverse rotation prevention state “R” normally but switched to the fixedstate “L” when an engine brake is effective.

In addition, FIG. 4 shows gear ratios (a rotational speed of the inputshaft 11/a rotational speed of the output member 13) and common ratios(a ratio of gear ratios between gear stages; a value obtained bydividing a gear ratio of a predetermined gear stage by a gear ratio of agear stage that is one speed level higher than the predetermined gearstage) at gear stages when a gear ratio h of the first planetary gearmechanism PG1 is 2.681, a gear ratio i of the second planetary gearmechanism PG2 is 1.914, a gear ratio j of the third planetary gearmechanism PG3 is 2.734, and a gear ratio k of the fourth planetary gearmechanism PG4 is 1.614. Accordingly, it can be understood that commonratios can be appropriately set.

Next, the two-way clutch F1 will be described in detail with referenceto FIG. 5 to FIG. 8. The two-way clutch F1 is switchable between a fixedstate in which the third connected body Ca-Cb is fixed to thetransmission case 10 and a reverse rotation prevention state in whichforward rotation of the third connected body Ca-Cb is allowed andreverse rotation is prevented.

As shown in cross sections in FIG. 5 and FIG. 6, the two-way clutch F1includes a fixing plate TW11 and a rotating plate TW12 fixed to thetransmission case 10. As shown in FIG. 7, the fixing plate TW11 isformed in a ring shape (donut shape). In addition, although not shown inFIG. 7, the rotating plate TW12 is formed in a ring shape (donut shape)similarly to the fixing plate TW11, and the fixing plate TW11 and therotating plate TW12 are disposed concentrically.

As shown in FIG. 5, on a facing surface TW11 a that faces the rotatingplate TW12 on the fixing plate TW11, a plate-like forward rotationprevention side swinging part TW13 in which an end TW13 a on the otherside (a direction in which the rotating plate TW12 rotates reversely) ina circumferential direction swings using an end on one side (a directionin which the rotating plate TW12 rotates forward) in the circumferentialdirection of the fixing plate TW11 as a shaft, and a plate-like reverserotation prevention side swinging part TW14 in which an end TW14 a onone side (forward rotation direction) in the circumferential directionswings using an end of the other side (reverse rotation direction) inthe circumferential direction of the fixing plate TW11 as a shaft areprovided.

In addition, on the facing surface TW11 a of the fixing plate TW11,concave accommodation units TW15 and TW16 in which the forward rotationprevention side swinging part TW13 and the reverse rotation preventionside swinging part TW14 can be accommodated are provided. On bottoms ofthe accommodation units TW15 and TW16, biasing members TW17 a and TW17 bincluding springs for biasing the swinging parts TW13 and TW14 areprovided so that the swinging ends TW13 a and TW14 a of thecorresponding swinging parts TW13 and TW14 protrude from theaccommodation units TW15 and TW16.

On a facing surface TW12 a that faces the fixing plate TW11 on therotating plate TW12, holes TW18 and TW19 are provided at positionscorresponding to the swinging parts TW13 and TW14. At the first holeTW18 provided at a position corresponding to the forward rotationprevention side swinging part TW13, a first engagement part TW18 ahaving a stepped shape that can be engaged with the swing end TW13 a ofthe forward rotation prevention side swinging part TW13 is provided suchthat it is positioned on the other side (a reverse rotation directionside) in the circumferential direction of the rotating plate TW12.

At the second hole TW19 provided at a position corresponding to thereverse rotation prevention side swinging part TW14, a second engagementpart TW19 a having a stepped shape that can be engaged with the swingend TW14 a of the reverse rotation prevention side swinging part TW14 isprovided such that it is positioned on one side (a forward rotationdirection side) in the circumferential direction of the rotating plateTW12.

As shown in FIG. 5 and FIG. 7, when the end TW13 a of the forwardrotation prevention side swinging part TW13 and the first engagementpart TW18 a are engageable and the end TW14 a of the reverse rotationprevention side swinging part TW14 and the second engagement part TW19 aare engageable, both forward rotation and reverse rotation of therotating plate TW12 are prevented. Accordingly, a state in which theends TW13 a and TW14 a and the engagement parts TW18 a and TW19 acorresponding thereto are engaged with each other is the fixed state inthe two-way clutch F1 of the present embodiment.

A switch plate TW20 is interposed between the fixing plate TW11 and therotating plate TW12. As shown in FIG. 7, the switch plate TW20 is formedin a ring shape (donut shape). On the switch plate TW20, notch holesTW20 a and TW20 b are provided at positions corresponding to theswinging parts TW13 and TW14.

A protrusion TW20 c that protrudes radially outward is provided at theouter edge of the switch plate TW20. As shown in FIG. 8, the switchplate TW20 is freely swingable with respect to the fixing plate TW11.

When the switch plate TW20 is swung from the fixed state shown in FIG. 7to the state shown in FIG. 8, as shown in FIG. 6, the first notch holeTW20 a corresponding to the forward rotation prevention side swingingpart TW13 exceeds the forward rotation prevention side swinging partTW13, and the forward rotation prevention side swinging part TW13 ispushed to the switch plate TW20 against the biasing force of the biasingmember TW17 a, and is accommodated in the accommodation unit TW15.Accordingly, engagement of the end TW13 a of the forward rotationprevention side swinging part TW13 and the first engagement part TW18 ais prevented. Accordingly, rotation of the rotating plate TW12 on theforward rotation side is allowed.

In addition, as shown in FIG. 8, in the second notch hole TW20 bcorresponding to the reverse rotation prevention side swinging partTW14, even when the switch plate TW20 is swung from the fixed stateshown in FIG. 7 to the state shown in FIG. 8, the end TW14 a can beengaged with the second engagement part TW19 a without accommodating thereverse rotation prevention side swinging part TW14 in the accommodationunit TW16.

Accordingly, the state shown in FIG. 6 and FIG. 8 is a reverse rotationprevention state in the two-way clutch F1 of the present embodiment.

Next, a hydraulic control device 100 included in the automatictransmission 3 of the present embodiment will be described withreference to FIG. 9. As shown in FIG. 9, the hydraulic control device100 controls operations of the parking piston 54 of the parking lockmechanism 40.

The hydraulic control device 100 includes an on and off type solenoidvalve 122C configured to supply a line pressure supplied from ahydraulic pump (not shown) to an oil passage L1 to a first locking oilchamber 112A and an on and off type solenoid valve 122E configured tosupply a line pressure of an oil passage L2 connected to a downstreamside of the oil passage L1 to a second locking oil chamber 112B. A checkvalve 124 is interposed in the oil passage L2 at a position upstreamfrom the solenoid valve 122E. When the solenoid valve 122C is opened, aline pressure is directly supplied to the first locking oil chamber112A. When the solenoid valve 122E is opened, a first ball valve 126A isopened. The solenoid valve 122C is a normally closed type, and thesolenoid valve 122E is a normally open type.

In addition, the hydraulic control device 100 includes an on and offtype solenoid valve 122F configured to supply a line pressure to a firstunlocking oil chamber 114A through an oil passage L3 and an on and offtype solenoid valve 122D configured to supply a line pressure of an oilpassage L4 branched upstream from the check valve 124 to a secondunlocking oil chamber 114B.

A line pressure is directly supplied to the second unlocking oil chamber114B through a brake cut valve 128 that is operated by the solenoidvalve 122D.

When the solenoid valve 122F is opened, a spool of a parking inhibitvalve 130 moves to the right side in FIG. 9 against a biasing force ofthe spring, and thus a line pressure is supplied to the first unlockingoil chamber 114A. On the other hand, when the solenoid valve 122F isclosed, a spool of the parking inhibit valve 130 is biased due to thespring and moves to the left side in FIG. 9, and thus a line pressure ofthe first unlocking oil chamber 114A is drained. The solenoid valve 122Fis a normally closed type, and the solenoid valve 122D is a normallyclosed type.

A second choke 132 narrowing a flow path is provided upstream from theparking inhibit valve 130 of the oil passage L3. The second choke 132 isconstituted by a slot groove of a separation plate. In this manner, whenthe second choke 132 is constituted by a slot groove of a separationplate, there is no need to separately provide a second choke member, itis possible to reduce the number of components, and it is possible tosimply assembly of the parking lock device.

In addition, a second check valve 134 is provided in parallel to thesecond choke 132 and prevents supply of a hydraulic pressured to thefirst unlocking oil chamber 114A and allows release of a hydraulicpressure from the first unlocking oil chamber 114A. When the secondcheck valve 134 is provided, it is possible to quickly release ahydraulic pressure.

An accumulation chamber 136 a of an accumulator 136 is connected to theoil passage L2 between the check valve 124 and the solenoid valve 122E.

A lock-up clutch shift valve 138 is connected to the oil passage L1downstream from the solenoid valve 122C, and a lock-up clutch pressureof an oil passage L5 is supplied to a lock-up clutch 2 a of the torqueconverter 2 which is a start mechanism through the lock-up clutch shiftvalve 138.

In addition, the first brake B1 is connected to an oil passage L6 whichis a hydraulic engagement device for shifting downstream from the checkvalve 124, and a linear solenoid valve 140G and the brake cut valve 128are disposed on the oil passage L6. Opening and closing of the brake cutvalve 128 are driven by the solenoid valve 122D. The linear solenoidvalve 140G includes an import 142 a, an outport 142 b, and a drain port142 c and can adjust a hydraulic pressure input from the import 142 aand output it from the outport 142 b, and release a hydraulic pressurefrom the outport 142 b through the drain port 142 c.

In addition, the hydraulic control device 100 includes a two-way piston212 that is engaged with the protrusion TW20 c of the switch plate TW20of the two-way clutch F1 and switches the switch plate TW20 between areverse rotation prevention state and a fixed state by a hydraulicpressure.

In the two-way piston 212, similarly to the parking piston 54, at oneend of the two-way piston 212 accommodated in a cylinder (not shown), afirst reverse rotation prevention oil chamber 222A and a second reverserotation prevention oil chamber 222B for moving the two-way piston 212to a side in a reverse rotation prevention state (“OWC” in FIG. 9) areprovided.

At the other end of the two-way piston 212, a first fixing oil chamber224A and a second fixing oil chamber 224B for moving the two-way piston212 to a side in a fixed state (“LOCK” in FIG. 9) are provided.

The first reverse rotation prevention oil chamber 222A is connected tothe oil passage L4. A line pressure can be supplied to the secondreverse rotation prevention oil chamber 222B through a solenoid valve122B. A line pressure can be supplied to the first fixing oil chamber224A through a linear solenoid valve 140B.

The linear solenoid valve 140B includes an import 144 a, an outport 144b, and a drain port 144 c, and can adjust a line pressure input from theimport 144 a and output it from the outport 144 b, and release ahydraulic pressure from the outport 144 b through the drain port 144 c.

A line pressure can be supplied to the second fixing oil chamber 224Bthrough a solenoid valve 122A.

Next, operations of the present embodiment having the aboveconfiguration will be described.

When a driver selects a D range or a R range using a shift operationunit such as a shift lever and a vehicle travels at a predetermined gearstage, a line pressure generated by a hydraulic pump driven by theinternal combustion engine is transmitted to the oil passage L1 and theoil passage L3, and a hydraulic pressure of the oil passage L1 istransmitted to the oil passage L2, the oil passage L4, and the oilpassage L6 through the check valve 124. The line pressure is supplied tothe oil passage L2 and the hydraulic pressure accumulates in theaccumulation chamber 136 a of the accumulator 136.

The normally closed type solenoid valve 122F is excited by energizationand is opened, and the normally closed type solenoid valve 122D is alsoexcited by energization and is opened. Then, when the solenoid valve122F is opened, the spool of the parking inhibit valve 130 moves to theright side in FIG. 9, and a line pressure of the oil passage L3 istransmitted to the first unlocking oil chamber 114A through the parkinginhibit valve 130. In addition, when the solenoid valve 122D is opened,a line pressure of the oil passage L4 is transmitted to the secondunlocking oil chamber 114B.

On the other hand, the normally closed type solenoid valve 122C isclosed when power supply is stopped, and the normally open type solenoidvalve 122E is excited by energization and closed. Then, when thesolenoid valve 122C is closed, oil in the first locking oil chamber 112Ais drained from the solenoid valve 122, and when the solenoid valve 122Eis closed, the first ball valve 126A is closed and thus oil in thesecond locking oil chamber 112B is drained from the first ball valve126A. As a result, the parking piston 54 moves to the left side in FIG.9 and parking lock is released (parking released state).

While a flow rate of oil that can pass through the solenoid valve 122Eis relatively low, a flow rate of oil that can pass through the firstball valve 126A that is opened or closed by the solenoid valve 122E isrelatively high. Therefore, it is possible to improve operationalresponsiveness of the parking piston 54 by interposing the first ballvalve 126A.

As described above, while the vehicle travels, the solenoid valve 122Cand the solenoid valve 122E are closed and the solenoid valve 122F andthe solenoid valve 122D are opened so that the parking piston 54 isoperated at an unlock position and parking lock can be released (parkingreleased state).

In addition, the parking lock mechanism 40 includes two locking oilchambers (the first locking oil chamber 112A and the second locking oilchamber 112B) at one end of the parking piston 54 and includes twounlocking oil chambers (the first unlocking oil chamber 114A and thesecond unlocking oil chamber 114E) at the other end thereof. Thereof,even when one of the solenoid valve 122F and the solenoid valve 122D isfixed in a closed state, and no hydraulic pressure is supplied to thefirst unlocking oil chamber 114A or the second unlocking oil chamber114B, or even when one of the solenoid valve 122C and the solenoid valve122E is fixed in an open state, and a hydraulic pressure is supplied tothe first locking oil chamber 112A or the second locking oil chamber112B, it is possible to operate the parking piston 54 at an unlockposition (notP position, a parking released state) without problem andensure redundancy.

Here, the solenoid valve 122F is opened at a first predetermined gearstage and the solenoid valve 122D is opened at a second predeterminedgear stage, and the first predetermined gear stage and the secondpredetermined gear stage partially overlap. Therefore, according to agear stage set at this time, there are cases in which a line pressure issupplied to only the first unlocking oil chamber 114A, a line pressureis supplied to only the second unlocking oil chamber 114B, and a linepressure is supplied to both the first unlocking oil chamber 114A andthe second unlocking oil chamber 114B. However, in all of the cases,since the parking piston 54 moves to the left side in FIG. 9 and parkinglock is released, there is no problem. Then, in an overlapping gearstage, since a line pressure is supplied to both the first unlocking oilchamber 114A and the second unlocking oil chamber 114B, even when thesolenoid valve 122F or the solenoid valve 122D fails and supply of aline pressure is stopped, parking lock remains in a deactivated state(parking released state) and redundancy is enhanced.

When the shift operation unit such as a shift lever is operated in a Prange and a vehicle is stopped while the internal combustion engineoperates, the solenoid valve 122C and the solenoid valve 122E areopened, and the solenoid valve 122F and the solenoid valve 122D areclosed. When the solenoid valve 122C is opened, a line pressure of theoil passage L1 is transmitted to the first locking oil chamber 112A, andwhen the solenoid valve 122E is opened, the first ball valve 126A isopened and a line pressure of the oil passage L2 is transmitted to thesecond locking oil chamber 112B.

On the other hand, when the solenoid valve 122F is closed, hydraulic oilin the first unlocking oil chamber 114A is discharged from the parkinginhibit valve 130, and when the solenoid valve 122D is closed, hydraulicoil in the second unlocking oil chamber 114B is discharged from thesolenoid valve 122D. As a result, the parking piston 54 moves to theright side in FIG. 9 and parking lock operates (parking locked state).

As described above, when the driver selects the P range using the shiftoperation unit while the internal combustion engine operates, thesolenoid valve 122C and the solenoid valve 122E are opened, and thesolenoid valve 122F and the solenoid valve 122D are closed. Therefore,the parking piston 54 can be operated at a parking lock position. Inthis case, since the parking lock mechanism 40 includes two locking oilchambers (the first locking oil chamber 112A and the second locking oilchamber 112B) and two unlocking oil chambers (the first unlocking oilchamber 114A and the second unlocking oil chamber 114B, even when one ofthe solenoid valve 122F and the solenoid valve 122D is fixed in an openstate, and a hydraulic pressure is supplied to the first unlocking oilchamber 114A or the second unlocking oil chamber 114B, or one of thesolenoid valve 122C and the solenoid valve 122E is fixed in a closedstate and no hydraulic pressure is supplied to the first locking oilchamber 112A or the second locking oil chamber 112B, it is possible tooperate the parking piston 54 at a parking lock position (P position)without problem and ensure redundancy (parking locked state).

When the shift operation unit is operated in the P range and ignition(vehicle power source) is turned off, the internal combustion engine isstopped and thus a line pressure due to the pump driven by the internalcombustion engine is removed. However, according to the presentembodiment, the parking lock mechanism 40 is operated due to a hydraulicpressure accumulated in the accumulator 136 without problem, and can beput into a parking locked state.

Then, when the solenoid valve 122E is opened, a hydraulic pressure ofthe accumulator 136 is transmitted to the second locking oil chamber112B. On the other hand, when the solenoid valve 122F is closed,hydraulic oil in the first unlocking oil chamber 114A is discharged fromthe parking inhibit valve 130, and when the solenoid valve 122D isclosed, hydraulic oil in the second unlocking oil chamber 114B isdischarged from the solenoid valve 122D. As a result, the parking piston54 moves to the right side in FIG. 9 and parking lock operates (parkinglocked state).

As described above, even when the P range is selected using the shiftoperation unit to turn ignition off and thus a line pressure is removed,the parking lock mechanism 40 can be operated due to a hydraulicpressure accumulated in the accumulator 136 without problem (parkinglocked state).

In addition, the vehicle of the present embodiment can perform idlingstop control, and the internal combustion engine stops during temporarystop such as during signal waiting, the pump also stops and a linepressure is removed.

Even when the internal combustion engine starts as return from idlingstop control, since a line pressure does not immediately rise, it is notpossible to supply a hydraulic pressure to the first brake B1 which is ahydraulic engagement device necessary for starting, and prompt startingmay be inhibited. However, according to the present embodiment, it ispossible to operate the first brake B1 without delay at a hydraulicpressure of the accumulator 136 remained in idling stop control.

More specifically, a hydraulic pressure accumulated in the accumulator136 is supplied from the oil passage L2 to the oil passage L6 at thesame time as return from idling stop control. In this case, since thesolenoid valve 122D interposed in the oil passage L4 is opened whenpower supply is stopped, a spool of the brake cut valve 128 moves to theleft side in FIG. 9. Therefore, when the linear solenoid valve 140Ginterposed in the oil passage L6 is opened to a predetermined degree ofopening, a hydraulic pressure accumulated in the accumulator 136 can besupplied to the first brake B1 and the vehicle can be started promptly.

While the operations of the first brake B1 as return from idling stopcontrol have been described above, the brake cut valve 128 can beoperated by the solenoid valve 122D to control the first brake B1 evenwhile the vehicle travels normally. When the spool of the brake cutvalve 128 moves to the left side in FIG. 9, communication between thelinear solenoid valve 140G and the first brake B1 is blocked and thesolenoid valve 122D is closed, and supply of a hydraulic pressure to thesecond unlocking oil chamber 114B is blocked. However, since it remainsat an unlock position due to a hydraulic pressure supplied to the firstunlocking oil chamber 114A, there is no risk of parking lock beingoperated (parking released state).

In addition, according to the present embodiment, the solenoid valve122C is also used for operating the lock-up clutch 2 a of the torqueconverter 2. That is, while the vehicle travels, since the solenoidvalve 122C is closed, a spool of the lock-up clutch shift valve 138moves to the right side in FIG. 9, and a lock-up clutch pressure issupplied to the lock-up clutch 2 a of the torque converter 2. When thesolenoid valve 122C is opened in this state, the spool of the lock-upclutch shift valve 138 moves to the right side in FIG. 9 and a hydraulicpressure of the lock-up clutch 2 a is discharged. Therefore, the lock-upclutch 2 a can be disengaged.

When the solenoid valve 122C is opened, a line pressure is supplied tothe first locking oil chamber 112A. However, in this case, since a linepressure is supplied to both the first unlocking oil chamber 114A andthe second unlocking oil chamber 114B, even when a line pressure issupplied to the first locking oil chamber 112A, the parking piston 54does not move to a parking lock position, and there is no risk ofparking lock being operated.

As described above, according to the parking lock mechanism 40 of thepresent embodiment, since the solenoid valve 122C and the solenoid valve122D that control operations of the parking piston 54 are also used forcontrol of the lock-up clutch 2 a of the torque converter 2 and controlof the first brake B1, it is possible to reduce the number of solenoidvalves and it is possible to simply the structure of the hydrauliccontrol device 100. In addition, since the accumulator 136 is used notonly for operation of parking lock but also for operation of the firstbrake B1 which is a hydraulic engagement device as return from idlingstop control, it is possible to reduce the number of accumulators and itis possible to further simplify the structure of the hydraulic controldevice 100.

Functions of the hydraulic control device 100 as a control unit are alsoperformed by the transmission control device ECU. The transmissioncontrol device ECU can receive current shift position information andshift switching request information based on an operation performed bythe driver using an operation unit.

In addition, the transmission control device ECU receives a parkinginput request instruction signal. Here, it is determined whether aparking input is necessary based on predetermined vehicle informationsuch as a travel speed of a vehicle that the control unit itself hasreceived and a parking input instruction signal (or a parking inputinstruction flag) may be issued.

In addition, in the transmission control device ECU, a countdown timeris provided, a numerical value is reduced from a preset initial value asthe time passes.

In addition, the transmission control device ECU can receive a signal ofa stroke sensor 56 provided at the parking piston 54 and determinewhether the parking piston 54 is positioned on a parking lock side orrelease side.

In addition, a hydraulic sensor (not shown; a state determination unit)is disposed on an oil passage through which a hydraulic pressure isguided to the first brake B1 via a branch path.

Here, in the hydraulic control device 100 of the present embodiment, ina non-traveling range such as a neutral range (an N range) or a parkingrange (a P range), there is a risk of the solenoid valve 122D (controlvalve) failing and a hydraulic pressure being supplied from the linearsolenoid valve 140G (proportional valve) to the first brake B1. In thenon-traveling range, when a hydraulic pressure is supplied to the firstbrake B1 and the first brake B1 is fastened, there is a risk of adriving force of the internal combustion engine being transmitted todrive wheels.

Accordingly, in order to prevent traveling due to a failure of thesolenoid valve 122D in the non-traveling range, when it is determinedthat the solenoid valve 122D fails (or always in the non-traveling rangeeven when there is no failure), supply of a hydraulic pressure to thefirst brake B1 through the linear solenoid valve 140G is prevented.Accordingly, even when the solenoid valve 122D fails in thenon-traveling range, supply of a hydraulic pressure to the first brakeB1 through the linear solenoid valve 140G can be prevented and drivingof the vehicle in the non-traveling range can be prevented.

On the other hand, when the linear solenoid valve 140G fails in thenon-traveling range (or always in the non-traveling range even whenthere is no failure), since a hydraulic pressure is supplied from thesolenoid valve 122D to the brake cut valve 128, the brake cut valve 128disconnects an oil passage between the linear solenoid valve 140G andthe first brake B1, and a hydraulic pressure supplied from the linearsolenoid valve 140G is prevented from being supplied to the first brakeB1.

In this manner, even when any of the solenoid valve 122D and the linearsolenoid valve 140G fails, it is possible to transmit a driving force ofthe internal combustion engine in the non-traveling range (for example,the N range) to drive wheels, and it is possible to improve safetyperformance of the vehicle.

In addition, in the hydraulic control device 100, a hydraulic switch(not shown; state determination unit) through which supply of ahydraulic pressure is stopped at the same time when the brake cut valve128 stops supply of a hydraulic pressure to the first brake B1 isprovided. The transmission control device ECU can determine whether thebrake cut valve 128 operates normally based on a hydraulic detectionresult of the hydraulic switch (not shown).

In addition, the transmission control device ECU of the presentembodiment performs a “2.5^(th) gear engagement process” in whichdriving is possible at a 2.5^(th) gear (refer to the collinear diagramin FIG. 11) set when the second clutch C2 is put into a connected stateand the second brake B2 is put into a fixed state under predeterminedconditions. The gear ratio of the 2.5^(th) gear is between gear ratiosof the second gear and the third gear.

The “2.5^(th) gear engagement process” will be described in detail withreference to the flowchart in FIG. 10. Here, the flowchart in FIG. 10 isrepeatedly performed at a predetermined control period (for example, 10milliseconds).

First, in STEP1, when the transmission control device ECU issues aninstruction to switch the first brake B1 to an engaged state, ahydraulic sensor (not shown) checks whether the first brake B1 isnormally switched to an engaged state. When the first brake B1 isswitched (when the state is not a released state; NO in STEP1), theprocess advances to STEP2, and the stroke sensor 214 provided in thetwo-way piston 212 of the two-way clutch F1 checks whether the two-wayclutch F1 is switched to a reverse rotation prevention state (OWCstate).

When the two-way clutch F1 is switched to a reverse rotation preventionstate (OWC state) (NO in STEP2), the process advances to STEP3, and ahydraulic switch (not shown) checks whether the brake cut valve 128 isswitched from a B1 cut state in which supply of a hydraulic pressure tothe first brake B1 is stopped to a B1 cut released state in which ahydraulic pressure is supplied to the first brake B1. Here, when supplyof a hydraulic pressure to the first brake B1 is blocked by the brakecut valve 128, according to a configuration of the hydraulic controldevice 100 of the present embodiment, no hydraulic pressure is suppliedto the first clutch C1 and the second brake B2, it is not possible toset a forward gear, and a vehicle cannot travel.

When the brake cut valve 128 is switched from a B1 cut state to a B1 cutreleased state, the process advances to STEP4, execution of the 2.5^(th)gear engagement process is prevented and the process at this time ends.

In STEP1, when the transmission control device ECU issues an instructionto switch the first brake B1 to an engaged state, the hydraulic sensor(not shown) confirms that the first brake B1 is not switched to anengaged state but remains in an open state (YES in STEP1), the processbranches to STEP5, and it is checked whether the range is a forwardtraveling range (D range) on the basis of received shift positioninformation. When the range is not a D range, since there is no need tomove a vehicle forward, the process advances to STEP4, execution of the2.5^(th) gear engagement process is prevented, and the process at thistime ends.

In STEP5, when the range is a D range, the process advances to STEP6,the 2.5^(th) gear engagement process” in which driving is possible atthe 2.5^(th) gear set when the second clutch C2 is put into a connectedstate and the second brake B2 is put into a fixed state is performed,and the process at this time ends.

In STEP2, when the two-way clutch F1 is not switched to a reverserotation prevention state (OWC state) (YES in STEP2), the processbranches to STEP5, and it is checked whether the range is a forwardtraveling range (D range) on the basis of the received shift positioninformation.

In STEP3, when the brake cut valve 128 is not switched from a B1 cutstate to a B1 cut released state (NO in STEP3), the process branches toSTEP5, and it is checked whether the range is a forward traveling range(D range) on the basis of received shift position information.

According to the automatic transmission 3 of the present embodiment,even when the first brake B1 cannot be switched to an open state becausethe automatic transmission 3 has failed so that the first brake B1remains in an engaged state, it is possible to set the 2.5^(th) gear asa preliminary gear stage that is a gear stage (a gear stage at whichdriving is possible at a speed equal to or lower than a speed of apredetermined gear stage) with a high gear ratio that is equal to orhigher than a gear ratio of the fifth gear as a predetermined gearstage. Therefore, according to the present embodiment, it is possible totravel uphill and it is possible to prevent deterioration of drivingperformance according to the preliminary gear stage.

In addition, according to the automatic transmission 3 of the presentembodiment, even when the two-way clutch F1 cannot be switched to areverse rotation prevention state due to a failure, it is possible toset the 2.5^(th) gear as a preliminary gear stage (a gear stage at whichdriving is possible at a speed that exceeds a speed of the startinggear) that is a gear with a lower gear ratio than the first gear as thestarting gear. Accordingly, even in a failure, it is possible to travelat a preliminary gear stage faster than the first gear as the startinggear, and it is possible to prevent deterioration of drivingperformance.

In addition, the automatic transmission 3 including the torque converter2 has been described in the present embodiment. However, the automatictransmission of the embodiments of the invention is not limited thereto.For example, the effects of the embodiments of the invention can beobtained in an automatic transmission in which an electric motor isprovided in place of the torque converter 2 and which is mounted in avehicle that travels using the internal combustion engine and theelectric motor.

In addition, the predetermined gear stage is not limited to the fifthgear and may be another gear stage. In addition, the preliminary gearstage is not limited to the 2.5^(th) gear, and may be a gear stage thatis set to a gear ratio equal to or greater than a gear ratio of thepredetermined gear stage. In addition, the first engagement mechanism isnot limited to the first brake B1, and may be another engagementmechanism. In addition, the second engagement mechanism is not limitedto the two-way clutch F1 and may be another engagement mechanism.

What is claimed is:
 1. An automatic transmission comprising: a pluralityof engagement mechanisms that are switchable between one state of anopen state and an engaged state or a fixed state and another statethereof; and a controller configured to instruct the engagementmechanisms to switch to the one state or the other state, wherein thecontroller sets a plurality of gear stages by changing a combination ofa plurality of engagement mechanisms that are put into the engaged stateor the fixed state among the engagement mechanisms, the automatictransmission includes a first engagement mechanism which is any one ofthe plurality of engagement mechanisms, wherein the first engagementmechanism is in one state of the open state and the engaged state or thefixed state in all of a first gear stage group from a first forward gearstage to a predetermined gear stage among the plurality of gear stages,and is in the other state at a gear stage with a higher speed than thepredetermined gear stage, and a state determination sensor configured todetect whether the first engagement mechanism has switched to the onestate, in response to determining that the controller instructs thefirst engagement mechanism to switch to the one state from the otherstate at the gear stage with the higher speed than the predeterminedgear stage and the state determination sensor confirms that the firstengagement mechanism is in the other state, the controller instructs theengagement mechanisms other than the first engagement mechanism toperform switching so that a preliminary gear stage is able to be set,wherein the preliminary gear stage is other than those in the pluralityof gear stages and is able to be set when the first engagement mechanismis in the other state, and the preliminary gear stage is a gear stagewith a low speed that has a gear ratio equal to or greater than a gearratio of the predetermined gear stage.
 2. The automatic transmissionaccording to claim 1, comprising a housing; an input unit that isrotatably disposed inside the housing; an output unit; and fourplanetary gear mechanisms comprising first to fourth planetary gearmechanisms that each include three elements including a sun gear, acarrier, and a ring gear; wherein the three elements of the thirdplanetary gear mechanism are a first element, a second element, and athird element in an arrangement order at intervals corresponding to agear ratio in a collinear diagram that is able to express a relativerotation speed ratio by a straight line, the three elements of thefourth planetary gear mechanism are a fourth element, a fifth element,and a sixth element in an arrangement order at intervals correspondingto a gear ratio in a collinear diagram, the three elements of the firstplanetary gear mechanism are a seventh element, an eighth element, and aninth element in an arrangement order at intervals corresponding to agear ratio in a collinear diagram, the three elements of the secondplanetary gear mechanism are a tenth element, an eleventh element, and atwelfth element in an arrangement order at intervals corresponding to agear ratio in a collinear diagram, the first element is connected to theinput unit, the tenth element is connected to the output unit, thesecond element, the fifth element, and the ninth element are connectedto form a first connected body, the third element and the twelfthelement are connected to form a second connected body, and the eighthelement and the eleventh element are connected to form a third connectedbody, the engagement mechanism includes three clutches comprising firstto third clutches, three brakes comprising first to third brakes, and atwo-way clutch, the first clutch is switchable between a connected statein which the first element and the third connected body are connectedand the open state in which the connection is disconnected, the secondclutch is switchable between a connected state in which the sixthelement and the second connected body are connected and the open statein which the connection is disconnected, the third clutch is switchablebetween a connected state in which the first element and the fourthelement are connected and the open state in which the connection isdisconnected, the first brake is switchable between the fixed state inwhich the seventh element is fixed to the housing and the open state inwhich the fixed state is released, the second brake is switchablebetween the fixed state in which the sixth element is fixed to thehousing and the open state in which the fixed state is released, thethird brake is switchable between the fixed state in which the fourthelement is fixed to the housing and the open state in which the fixedstate is released, the two-way clutch is switchable between a reverserotation prevention state in which forward rotation of the thirdconnected body is allowed and reverse rotation is prevented and thefixed state in which rotation of the third connected body is prevented,the first engagement mechanism is the first brake, the one state is theopen state, and the preliminary gear stage is a gear stage set when thesecond clutch and the third brake are put into the engaged state and theother engagement mechanisms are put into the open state.